Application Areas - Filter Media Testing

Filter Media

Solutions for Manufacturers and End Users Quality Assurance

High Efficiency filter medias for use in pleated, flat or other formats in filter devices are designed using a range of base constructions, from fibrous structures made from glass or synthetic micro or nano fibres, cast polymeric membranes, sintered metals / polymers through to track etched membranes.

Surface modification to add beneficial surface properties such as addition of low surface tension binders, hydrophobic additives or the treatment with plasma processes to modify surface chemistry, all change the filtration characteristics.

The ability to test filter medias under a range of flowing conditions and with differing challenge aerosols allows media developers to modify their formulations to achieve required characteristics in terms of efficiency, permeability and loading characteristics.

Industry standards such as EN1822, EN779 and ANSI/ASHRAE 52.2 require levels of performance to be achieved to meet a specific grading within their defined efficiency bands.

The performance of cleanable medias for use in, for example, reverse flow / pulse jet filter bag systems is dependent on the dust release characteristics of the media itself. As the filter progresses through many regeneration cycles, it ages and the regeneration proves less efficient, so the differential pressure across the media post regeneration increases. The filtration efficiency is also dependent on the cycle, typically with lower efficiency seen after the reverse cleaning pulse.

Our range of MFP Filter Media test systems allows manufacturers and media users to validate and verify filter media performance across a range of particle sizes and using different challenge materials.

The MMTC Filter Media Test range is designed specifically for cleanable media validation and allows testing in accordance with the VDI/DIN 3926 Guideline, type 1 and 2.

HEPA / ULPA Definitions

The standardisation of high efficiency filtration specification and testing is complex at the moment. Several standards are applied across the world and harmonisation is proving difficult. In Europe perhaps the primary document defining high efficiency filter performance is the EN1822 High efficiency air filters (EPA, HEPA and ULPA) Series which defines:

  • EPA — Efficient Particulate Air
  • HEPA — High Efficiency Particulate Air
  • ULPA — Ultra Low Penetration Air

It is divided into five parts:

  • Part 1:2009 — Classification, performance testing, marking
  • Part 2:2009 — Aerosol production, measuring equipment, particle counting statistics
  • Part 3:2009 — Testing flat sheet filter media
  • Part 4:2009 — Determining leakage of filter elements (scan method)
  • Part 5:2009 — Determining efficiency of filter elements

Also often referenced in Europe is:

  • EN 779:2002 Particulate air filters for general ventilation. Determination of the filtration performance currently under review

The ’equivalent’ standard for the application in the US, although quite different in its methodology is:

  • ANSI/ASHRAE 52.2 — 2007 Method of Testing General Ventilation Air—Cleaning Devices for Removal Efficiency by Particle Size

EN1822-1:2009 defines current grades as the following, with the aerosol used to challenge the filter under test at the MPPS (Most Penetrating Particle Size):

Group
Filter Class
Integral Value
Local Value
Filtration Efficiency
Penetration
Filtration Efficiency
Penetration
EPA
E10
85%
15%
E11
95%
5%
E12
99.5%
0.5%
HEPA
H13
99.95%
0.05%
99.75%
0.25%
H14
99.995%
0.005%
99.975%
0.025%
ULPA
U15
99.9995%
0.0005%
99.9975%
0.0025%
U16
99.99995%
0.00005%
99.99975%
0.00025%
U17
99.999995%
0.000005%
99.9999%
0.0001%

The MPPS is generally found to be somewhere between 0.1 and 0.3µm, dependant on the particular media on test and the flow velocity through it.